In a typical cellular radio system, wireless terminals (also referred to as user equipment unit nodes, UEs, and/or mobile stations) communicate via a radio access network (RAN) with one or more core networks. The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a radio base station (also referred to as a RAN node, a “NodeB”, and/or enhanced NodeB “eNodeB”). A cell area is a geographical area where radio coverage is provided by the base station equipment at a base station site. The base stations communicate through radio communication channels with UEs within range of the base stations.
Moreover, a cell area for a base station may be divided into a plurality of sectors surrounding the base station. For example, a base station may service three 120 degree sectors surrounding the base station, when the base station providing a respective directional transceiver and sector antenna array for each sector. Stated in other words, a base station may include three directional sector antenna arrays servicing respective 120 degree base station sectors surrounding the base station.
Multi-antenna techniques can significantly increase capacity, data rates, and/or reliability of a wireless communication system as discussed, for example, by Telatar in “Capacity Of Multi-Antenna Gaussian Channels” (European Transactions On Telecommunications, Vol. 10, pp. 585-595, November 1999). Performance can be improved if both the transmitter and the receiver for a base station sector are equipped with multiple antennas (e.g., an sector antenna array) to provide a multiple-input multiple-output (MIMO) communication channel(s) for the base station sector. Such systems and/or related techniques are commonly referred to as MIMO (Multiple-Input-Multiple-Output). The HSPA (High Speed Packet Access) standard is currently evolving with enhanced MIMO support and MIMO antenna deployments. A spatial multiplexing mode is provided for relatively high data rates in more favorable channel conditions, and a transmit diversity mode is provided for relatively high reliability (at lower data rates) in less favorable channel conditions.
In a downlink (DL) from a base station transmitting from a sector antenna array over a MIMO channel to a wireless terminal in the sector, for example, spatial multiplexing (or SM) allows the simultaneous transmission of multiple symbol streams over the same frequency from the base station sector antenna array for the sector. Stated in other words, multiple symbol streams are transmitted from the base station sector antenna array for the sector to the wireless terminal over the same downlink time/frequency resource element (TFRE) to provide an increased data rate. As used herein, a time/frequency resource element may also be referred to as a transmission time interval or TTI. In a downlink from the same base station sector transmitting from the same sector antenna array to the same wireless terminal, transmit diversity (e.g., using space-time codes) is the simultaneous transmission of the same symbol stream over the same frequency from different antennas of the base station sector antenna array. Stated in other words, the same symbol stream is transmitted from different antennas of the base station sector antenna array to the wireless terminal over the same time/frequency resource element (TFRE) to provide increased reliability of reception at the wireless terminal due to transmit diversity gain.
To further increase throughput at a sector/cell edge (also referred to as a soft handover or border area) using High Speed Downlink Packet Access (HSDPA), Multi-Flow-HSDPA (MF-HSDPA, also referred to as Multi-Flow-HSDPA or MP-HSDPA) has been proposed for 3rd Generation Partnership Project (3GPP) communications. In MF-HSDPA, transport data blocks of a data stream are transmitted from two different sectors/cells of the same or different base stations to a same wireless terminal in a border area between the sectors/cells. Intra NodeB aggregation (also referred to as intra node Multi-Flow communications) occurs when different transport data blocks of a data stream are transmitted from two different sectors of a same base station to a wireless terminal, and Inter NodeB aggregation (also referred to as inter node Multi-Flow communications) occurs when different transport data blocks of a data stream are transmitted from sectors/cells of different base stations to a wireless terminal. MF-HSDPA may thus provide advantages of parallel data streams like MIMO where the spatially separated antennas are taken from different sectors/cells.
When MF-HSDPA is used to transmit transport data blocks from different base stations to a wireless terminal during a same time resource element (also referred to as a transmission time interval or TTI), neither base station may be aware of how many transport data blocks were transmitted by the other base station. Accordingly, it may be difficult to provide efficient feedback from the wireless terminal to the network regarding the transport data blocks of a multi-flow transmission.